Flower:

Separate male and female flowers on separate plants (dioecious). Female flowers are clustered at the tips of stalks arising from leaf axils and at branch tips, with 10 to 50 pairs of flowers in a cluster, each pair subtended by a green to yellowish bract, mostly blunt at the tip and dotted with yellow glands at the base. Female flowers have 2 long thread-like styles and no petals. Female clusters are up to ¾ inch long, with a series of rounded, hairless bracts around the base.

Male flowers are in branching clusters arising from upper leaf axils and at branch tips, with 20 to 100+ flowers in a cluster. Male flowers have 5 spreading sepals, 5 short stamens with creamy yellow tips dotted with yellow glands, and are short-stalked.

Leaves and stems:

Leaves are opposite, 1 to 6 inches long, the largest leaves as wide as long or nearly so, sharply toothed around the edges, broadly heart-shaped in outline. Most leaves have 3 to 7 lobes, the lobes with sharply pointed tips; some leaves are unlobed. The dominant number of lobes on a plant depends on the variety (see Notes below) but is usually 3.

The upper leaf surface is mostly hairless, the lower surface variously softly hairy along the veins, sometimes also on the surface. Yellow glands dot the lower surface. Leaf stalks are usually shorter than the blade. Leaf nodes are minutely hairy. Surrounding the stalk at the leaf node is a pair of leafy appendages (stipules) that are more or less triangular, soon split down the middle, and eventually wither away.

Stems are branched and green. Stems and leaf stalks have scattered downward-pointing hairs that grab onto trees and other structures and allow the vine to climb.

Fruit:

The floral bracts enlarge and create a cone-like structure up to 3 inches long, holding the yellowish, gland-dotted seeds. The cones ripen to straw-colored then brown and persist through winter.

Notes:

Common Hops is a confused (or confusing, depending on your point of view) species. There are currently 4 recognized varieties, though a recent study recommends changing them to 4 separate species, one of which is European in origin and the rest native to North America. They are distinguished from each other by, among other things, the density of hairs along the leaf midrib and density of glands on the lower leaf surface (10x or greater magnification recommended). Start counting.

• The European var. humulus (H. lupulus) is the hops cultivated for beer making, the resinous dots giving it its distinctive aroma and flavor; it has 15 to 25 hairs per linear cm on the midrib and fewer than 20 glands per square cm on the surface, where the other vars have 25 or more glands.
• For var. neomexicanus (H. neomexicanus), there are more than 30 glands per sq. cm and the largest leaves have 5 or 7 lobes, where 3 lobes is more common for the other vars.
• For var. pubescens (H. pubescens), leaf hairs are spreading, the leaf midrib has more than 100 hairs per linear cm, hairs are on the surface as well as veins.
• For var. lupuloides (H. lupuloides), leaf hairs are appressed, the leaf midrib has 20 to 75 hairs per linear cm.

The DNR currently lists both var. pubescens and var. lupuloides present in Minnesota. There are no Bell Herbarium records for var. pubescens and the DNR does not currently list any specific counties for it, but more than half the existing records have no var designation at all and at least some portion are likely the European species. With this state of things it is not surprising the national distribution map is not distinguishing the native and European vars. Maybe some day it will be sorted out. Of note is we encountered Hops in Aitkin County that had predominantly 5 or 7 lobes, which is apparently atypical for either pubescens or lupuloides but not neomexicanus., though there are currently no records of neomexicanus in MN. That site is worth a revisit.

The invasive Japanese Hops (Humulus japonicus, a.k.a. Humulus scandens) is very similar to Common Hops, and is distinguished by hairier stems, leaf stalks mostly longer than the blade, leaves with 5 to 9 lobes (none unlobed, few 3-lobed near the stem tip), stiff leaf hairs, and stipules and floral bracts with a fringe of hairs around the edge. Japanese Hops is also an annual, where Common Hops is perennial.